"He's more recently self-injured seriously for a period of several minutes in the toilet of his own accommodation, resulting in a three-month hospital admission," Peter Curotte told Lateline.

The one defining event over the years was when Alexander told his parents he was raped in the shower and forced to perform oral sex on his carer a number of times when he was 12.

"Autistic people don't usually lie, they don't understand the concept of lying," Paula Curotte said.

"Alexander has been consistent all these years and has never named anybody else or got confused about the details.

"We have no doubt at all that this happened to our son."

As soon as Alexander made the rape claims, the family complained to the Department of Human Services (DHS) and police.

No-one was charged and Alexander's emotional state has gone steadily downhill since.

"When we made the disclosure and to this date, which is a period of 12 or 13 years, no support has been offered to Paula or myself or the children from the Department of Human Services in the matter of Alexander alleging sexual abuse by a DHS worker," Mr Curotte said.

Alexander's parents say a few years after the alleged rape other staff members restrained him during a violent episode by holding him under a blanket until he passed out.

Later medical exams revealed he had had a stroke and he remains partially paralysed down one side.

"We feel a lot of his distress and self-harming came about from that time - often you don't realise these things until retrospectively," she said.

'Tip of the iceberg'

I'm suffering, my sister is suffering and we're sitting here waiting for an answer but nothing is happening.

Vicki

Kevin Stone, the executive officer of disabled advocacy group Valid, says they aware of similar cases.

"We know it's happening out there," he said.

"We think it's the tip of the iceberg. We think it's happening in far more services than we dare think about.

"It's not only happening in Victoria, it's happening across the country."

In January this year, Vicki, who cannot be identified for legal reasons, was contacted by the charity organisation caring for her disabled sister.

What she was heard her sister repeat was devastating.

"He touched her here, kissed her, touched her here, there," she said.

"He tried to put [his genitals] in her mouth... [it was] sickening."

She says her sister's testimony is all on the record with police.

The police investigation into the alleged repeated rapes of Vicki's sister and the alleged assault of another client by a male carer is ongoing.

And so is the victim's trauma.

Vicki's sister has been told she may need need to have surgery as a result of the alleged abuse.

"Because of her sexual abuse she may have had an anal tear and therefore bleeding," Vicki said.

Vicki feels because her sister is disabled, she is not being taken seriously.

"I'm suffering, my sister is suffering and we're sitting here waiting for an answer but nothing is happening," she said.

Cover-up allegations

Staff that complained ... [were] thanked for bringing it to management attention and then very quickly told 'well, we wouldn't want this to get out, would we?'

Peter Cross

Another case involves the alleged rapes of four disabled people at a care facility in Melbourne run by the Yooralla Organisation.

A former staff member has now been charged.

Peter Cross, who is a guardian of one of the women who complained about sexual assaults, along with some staff members, says management tried to cover up the alleged abuse.

"Staff that complained and were spoken to by Yooralla management, and as people have said, [they were] patted on the head, thanked for bringing it to management attention and then very quickly told 'well, we wouldn't want this to get out, would we?'"

Mr Cross has been in constant conflict with Yooralla over their handling of complaints and management style.

He and other families whose loved ones have allegedly been abused have recently formed a lobby group.

"We're going to be campaigning for a royal commission into disability services," he said.

The allegations of abuse at Yooralla came to light when resident Craig McDonnell spoke up.

He says residents come second.

"They are negligent about the people that they're caring about," he said.

"That's what they're supposed to care about, not themselves."

Victoria's Minister for Human Services Mary Wooldridge was not available for interview but in a statement told Lateline that abuse and misconduct is not tolerated.